Computer assisted design (CAD) and computer assisted manufacture (CAM) have been available for a significant period of time. Typically these processes are used to design a part, typically metal, and to assist in the fabrication of the part, typically through the use of numerically controlled machine tools. The specification of the material from which the part is to be manufactured is typically selected by a supervising engineer.
U.S. Pat. No. 6,766,207 issued Jul. 20, 2004 to Sato et al., assigned to Fujitsu Limited is representative of design of a “soft” mechanical part. The attributes referred to in the specification are not the physical properties of the polymer but rather the attributes of the part (e.g. shape, revision etc.). See the description of FIG. 14.
U.S. Pat. No. 6,136,235, issued Oct. 24, 2000 to Saito et al., assigned to Cannon Kabushiki Kaisha discloses a computer assisted method to determine the stresses on a plastic part when it is being molded. The patent teaches that the process is used to predict the warpage of a part, and particularly a fiber reinforced part. Based on the predictions when the part goes into manufacture if there are difficulties “quick counter measures” can be made. From the thrust of the specification the counter measures are likely to be a redesign of the part rather than selecting a different resin.
U.S. Pat. No. 6,187,601, issued Feb. 13, 2001 to Hu et al., assigned to Ford Global Technologies, Inc. discloses a method to design a plastic encapsulated power integrated circuit and a lead frame. The process includes evaluating the likelihood of peeling and shearing of the plastic from the lead substrate. The design has various radii of curvature and the issue is delamination and cracking at, or along, the radius of curvature. A finite element analysis of the design for various combinations of the plastic and lead part is conducted to determine the likelihood of cracking. This is used to select an appropriate combination of materials or to modify the design to minimize stress and select a preferred combination of materials. The parts are rigid and are not intended to flex to any significant extent during use.
U.S. Pat. No. 6,874,370, issued Apr. 5, 2005 to Vachon, teaches a method to calculate the strain and fatigue damage of a part undergoing repetitive deformation using finite element analysis and a detectable physical observation of the product under deformation. Rather than the selection of a preferred material of construction, the patent is more focused on methods of detecting deformation and then predicting cumulative strain and fatigue damage.
There are a number of patents disclosing polyolefin gasoline cans having an accordion type nozzle (e.g. U.S. Pat. No. 5,350,091 issued Sep. 27, 1994 to Leete et al.). Such nozzles are in an environment which tends to induce stress cracking and it is helpful to have some means of predicting plastics which would have useful life in the part (nozzle).
Snap lids are also used in a number of applications. While the design appears quite simple, in fact is it complex having a hinge formed from a plastic web. Again it would be useful to have a method to determine a preferred resin.
The present invention seeks to provide a computerized method to select a plastic to be used to form a non woven plastic web.